diff --git a/io_linux.h b/io_linux.h
index 4efe637..b686c13 100644
--- a/io_linux.h
+++ b/io_linux.h
@@ -6,24 +6,26 @@
 
 /* Hmm.  These constants vary a bit between systems. */
 /* (__sh__ includes both sh and sh64) */
-#if defined(__alpha__) || defined(__sparc__) || defined(__mips__) || defined(__ppc__) || defined(__ppc64__) || defined(__sparc64__)
-#define CHRONY_IOC_NRBITS	8
-#define CHRONY_IOC_TYPEBITS	8
-#define CHRONY_IOC_SIZEBITS	13
-#define CHRONY_IOC_DIRBITS	2
-
-#define CHRONY_IOC_NONE         1U
-#define CHRONY_IOC_READ         2U
-#define CHRONY_IOC_WRITE        4U
-#else
+#if defined(__i386__) || defined(__sh__)
 #define CHRONY_IOC_NRBITS	8
 #define CHRONY_IOC_TYPEBITS	8
 #define CHRONY_IOC_SIZEBITS	14
 #define CHRONY_IOC_DIRBITS	2
 
-#define CHRONY_IOC_NONE	        0U
+#define CHRONY_IOC_NONE	0U
 #define CHRONY_IOC_WRITE	1U
-#define CHRONY_IOC_READ	        2U
+#define CHRONY_IOC_READ	2U
+#elif defined(__alpha__) || defined(__sparc__) || defined(__mips__) || defined(__ppc__) || defined(__ppc64__) || defined(__sparc64__)
+#define CHRONY_IOC_NRBITS	8
+#define CHRONY_IOC_TYPEBITS	8
+#define CHRONY_IOC_SIZEBITS	13
+#define CHRONY_IOC_DIRBITS	2
+
+#define CHRONY_IOC_NONE        1U
+#define CHRONY_IOC_READ        2U
+#define CHRONY_IOC_WRITE       4U
+#else
+#error "I don't know the values of the _IOC_* constants for your architecture"
 #endif
 
 #define CHRONY_IOC_NRMASK	((1 << CHRONY_IOC_NRBITS)-1)